Diagram 1 is an internal layout diagram of a stepping motor driven exhaust gas re-circulation valve. The stepping motor is a device for controlling the valve by electrical motive force.
In the diagram, reference numeral 1 represents the housing (valve body), and comprises an inlet port 2 connected to the engine exhaust system (not shown), an outlet port 3 connected to the engine air intake system (not shown) and a re-circulation pathway 4. The valve seat 6 is press-fitted into the re-circulation pathway and prevents the rollpin 13 from detaching. 9 is a bush acting as a bearing, 8 is a holder for preventing the build up of deposits on the bush 9 and is fitted on the same axis as the valve seat 6 between the housing 1. 5 is a valve which is disposed in abutment with the valve seat 6 and is secured to the valve shaft 7 by caulking. The valve shaft 7 extends through the bush 9 and a spring holder 10 and washer 50 are fixed to its other end by caulking. 12 is a spring which is provided between the spring holder 10 and the housing 1 in a compressed state with the direction of force being in the direction of valve closure. 14 is a cooling passage for cooling the motor and the body of the valve.
20 is the body of the stepping motor and is mounted on the housing 1 by a mounting screw so that the axes correspond. 22 is a bobbin around which the coil 23 is entwined, and which is provided with a yoke 24 and yoke 25 providing a magnetic circuit around the outer circumference. 29 is a terminal which is electrically connected to the coil 23 and which forms the connector element with the motor housing 21. 27 is a plate which shields magnetically the two coil sections. 26 is a plate preventing the seepage of resin into the inner part of the coil when the motor housing is armor molded.
31 is a magnet. 32 is a rotor which protects the magnet 31 and forms a stopper 32b in the axial direction of the motor shaft and the threaded section 32a which meshes with the threaded section 33a of the motor shaft in the inner section. 30 are bearings fitted to both ends of the rotor 32. 28 is platespring which pressures the side of the bearing. 33 is a reciprocating motor shaft which converts the rotations of the rotor 32 to rectilinear motion by the threaded sections 32a, 33a. 34 is a stopper pin which is press fitted into the motor shaft 33, 41 is a motor bush which functions as a bearing for the motor shaft 33 and prevents rotation around the D hole.
40 is a motor holder disposed between the housing 1 so as to be concentric with the motor housing 21 and which protects the bearing 30 and the motor bush 41. The spring holder 42 and the joint 43 are fixed to the distal end of the motor shaft 33 by caulking. 44 is a spring which is compressed between the spring holder 42 and the motor holder 40 so that the direction of the force is in the direction of valve opening 5.
The operation of the valve will be explained on the basis of the force corresponding to the position of the valve in diagram 2.
With reference to diagrams 1 and 2, when the valves are opened starting from a position of total valve closure, the rotor 32, including the magnet 31, rotates in the direction of valve opening in a step-wise fashion in response to electrical pulses sent from the control unit (not shown) in the terminal 29. The number of steps correspond with the number of pulses and constitutes precise open loop control. The step-wise rotations are converted into rectilinear motion by the threaded section 32a of the rotor 32 and the threaded section 33a of the motor shaft 33. The motor shaft moves in the direction of valve opening (shown in the lower part of the diagram). At this stage, the movement of the motor shaft 33 is assisted by the force of the spring 44. At the moment when the joint 43 and the spring holder 10 are in abutment as a result of this motion, since the force of the springs is added, the necessary force to move the motor becomes the difference of the springs. Further movement entails increased load including the spring constant of the springs.
When the valves are closed, the above process is reversed. The rotor 32 including the magnet 31 rotates step-wise in the direction of valve closure in response to: electrical pulses sent from the control unit (not shown) in the terminal 29. At the moment when the joint 43 and the spring holder 10 become detached as the closure process continues, the load of the spring 44 is added to the motor shaft 33 and the load of the spring 12 is added to the valve 5 as a closure force.
A numerical example of the above process will now be discussed. If the setting of the spring is set using the open valve position as a standard, then the spring 12 in the set position has a load of 2 Kg f, and a spring constant of 0.05 Kg f/mm. The spring 44 in the set position has a load of 1.2 Kg f and a spring constant of 0.05 Kg f/mm. If the stroke from motor shaft activation to valve opening is given as 1 mm, and from opened to totally opened as 4.5 mm, then as shown in Diagram 2, the maximum load on the motor at point of activation and point of total opening is equal to 1.25 Kg f. In addition the force of closure of the valve is 2 Kg f and is equal to the load in the set position of the spring A12.
Now referring to the conventional organization of the device (without the spring 44), since the load condition of the spring 12 is the same, in order to achieve the same closure force as in the second diagram, the force generated by the motor must reach a maximum of 2.225 Kg f ( when the valve is completely opened).
As conventional exhaust gas re-circulation valves are constructed in the above manner, although it is possible to cool the valve body and the stepping motor with coolant introduced into the cooling passage 14, the valve body must be sufficiently large to form the cooling passage 14 around the housing 1. Furthermore a pipe is necessary to connect the coolant passage 14 to the engine coolant system which increases the number of necessary parts. The separate coolant system increases the complexity of the layout, all of which increases the price.
The present invention is proposed to solve the above problems. It is a purpose of the present invention to provide, without the need for a separate cooling system, a mounting device for an exhaust gas re-circulation valve which prevents overheating of the valve body and the stepping motor, which controls the movement of the exhaust gas re-circulation valve, due to high temperature exhaust gas. The invention also involves both a reduction in the size of the exhaust gas re-circulation valve and in the costs involved.
It is a further object of the present invention to enable easy mounting of the exhaust gas re-circulation valve on the engine block and to prevent the high temperature of the exhaust gas from being transmitted to the stepping motor.
Further objects include reductions in costs and the use of the invention in conjunction with a seal in the mounting part which prevents the valve seat from dislodging.